High voltage power transmission lines carrying voltages in the hundreds of kilowatt range have been constructed to extend from spaced towers or poles (hereinafter “towers”). Towers having vertically spaced apart cross arms are frequently employed for supporting multiple high voltage electrical conductors. The conductors are typically supported under the arms of such towers using at least one suspension insulator for each conductor.
The manner in which the cross arms are connected to the towers and the types of towers and cross arms utilized vary depending upon such factors as the number and weight of the conductors to be supported, the spacing between towers, the topography of the land and the environmental conditions to which the tower and arms will be subjected. Thus, the manner of connection between the cross arms and the tower may be as simple as utilizing a cross arm bolt assembly wherein a bolt extends horizontally through the cross arm and the tower or as sophisticated as utilizing lattice type towers having lattice type arms and bridges, e.g., formed of channel or angle iron, secured to opposite faces of the tower. One type of tower and cross arm often utilized for long distance transmission and heavy, high voltage carrying conductors comprises polygonal, tubular steel towers having polygonal, tubular steel cross arms supporting the conductors at their outer ends and being affixed to the tower via welded connectors. In one frequently utilized configuration, a mounting bracket is welded to the tower end of each arm and the mounting bracket is bolted to the tower.
It has recently been observed, particularly in high wind, flat, open areas such as are encountered in states such as Texas, that the winds cause the cross arms to vibrate at dangerous vibration frequencies and the vibration of the arms, together with the heavy weight of the conductors at the ends of the arms, causes the welded connection of the arms to the mounting brackets to crack. When this occurs the entire arm and mounting bracket must be replaced. It will be appreciated that high voltage electrical transmission lines extend over long distances and utilize hundreds of towers supporting thousands of arms. When weld cracking occurs frequently on numerous cross arms, a major problem exists necessitating a repair undertaking involving considerable expense. Moreover, replacing the arm and mounting bracket where there is a cracked weld may only be a temporary solution since it does not prevent the damage from recurring to the same or a different arm.
Accordingly, there exists a need for a method for retrofitting and upgrading the hundreds of existing towers to prevent wind induced vibration-damage to the weld or welds in the welded connection between the conductor supporting cross arm and the tower, and apparatus for accomplishing this method, without the need for field welding or in any way compromising the structural integrity of the towers.